Background: According to the limited number of studies in this field as well as the contradiction in the results of these studies, we performed this study to investigate corpus luteum RI in normal and abnormal pregnancies of the first trimester and comparison between the two groups. Methods: In this cross-sectional study, 50 abnormal pregnant and 50 normal pregnant women were selected and were underwent ultrasonography. Blood flow impedance was measured by using the PSV, EDV and RI and the average of three times measuring was considered as the final RI in each patient. Corpus luteum diameter and PSV were also measured in each patient and compared between the two groups. Results: The mean of Resistance index, peak systolic velocity and Diameter in the normal and abnormal groups were 0.509 ± 0.068 (p=0.308), 28.71 ± 13.83 and 25.16 ± 13.36(p=0.207), 19.85 ± 5 and 18.86 ± 5.17 (p=0.343) respectively. Conclusion: The results of our study showed that the profile of corpus luteum in normal and abnormal pregnancies was not differing significantly.